1. Field of the Invention
The present invention relates to a photothermographic material and an image forming method using the same.
2. Description of the Related Art
In recent years, in the field of films for medical diagnosis and in the field of films for graphic arts, there has been a strong desire for decreasing the amount of processing liquid waste from the viewpoints of protecting the environment and economy of space. Technology is therefore required for light-sensitive photothermographic materials which can be exposed effectively by laser image setters or laser imagers and thermally developed to obtain clear black-toned images of high resolution and sharpness, for use in medical diagnostic applications and for use in photographic technical applications. The light-sensitive photothermographic materials do not require liquid processing chemicals and can therefore be supplied to customers as a simpler and environmentally friendly thermal processing system.
While similar requirements also exist in the field of general image forming materials, images for medical imaging in particular require high image quality excellent in sharpness and granularity because fine depiction is required, and further require blue-black image tone from the viewpoint of easy diagnosis. Various kinds of hard copy systems utilizing dyes or pigments, such as ink jet printers and electrophotographic systems, have been marketed as general image forming systems, but they are not satisfactory as output systems for medical images.
Thermal image forming systems utilizing organic silver salts are known. In particular, photothermographic materials generally have an image forming layer in which a catalytically active amount of a photocatalyst (for example, silver halide), a reducing agent, a reducible silver salt (for example, an organic silver salt), and if necessary, a toner for controlling the color tone of developed silver images are dispersed in a binder. Photothermographic materials form black silver images by being heated to a high temperature (for example, 80° C. or higher) after imagewise exposure to cause an oxidation-reduction reaction between a silver halide or a reducible silver salt (functioning as an oxidizing agent) and a reducing agent. The oxidation-reduction reaction is accelerated by the catalytic action of a latent image on the silver halide generated by exposure. As a result, a black silver image is formed on the exposed region. Further, the Fuji Medical Dry Imager FM-DPL is an example of a medical image forming system using photothermographic materials that has been made commercially available.
In addition to photographic properties, film physical properties of surfaces are very important for the photothermographic material. For example, production of the photothermographic material comprises steps of coating solutions on a long roll support, drying the coated film, winding the dried film, and finishing such as slitting and cutting to provide a roll state or a sheet state. In the above steps, the material is conveyed at a high speed while being wound or unwound. Moreover, in an image forming step, the material is also conveyed at a high speed in a sheet state or a roll state. A method of providing surface roughness by coating matting agents on the film surface to decrease contact area and thereby reduce conveying resistance has been generally employed for conventional photographic materials and is also effective for photothermographic materials to improve conveying suitability thereof.
Japanese Patent Application Laid-Open (JP-A) No. 2004-309641 discloses the use of antistatic agents to prevent electrostatic trouble occurring during conveying of a film at a high speed. As the antistatic agent used for the material, the use of a fluorocarbon surfactant is disclosed. All patents, patent publications, and non-patent literature cited in this specification are hereby expressly incorporated by reference herein.
On the other hand, the manufactured photothermographic materials have such a problem that adhesion to themselves or to each other occurs during storage in a roll state or when the materials are stacked and stored in a sheet state. To prevent this problem, addition of matting agents to the outermost layer of the material is widely employed.
All chemicals required for image formation are incorporated within the coated layers of a photothermographic material in advance. After image formation, these chemicals remain in the material as reaction products or unreacted components. As a result, all of the chemicals exert complicated influences on photographic properties and film physical properties of the photothermographic materials, and also on the storage stability thereof.
Therefore, it is desired that surface compositions of the photothermographic materials satisfy not only the film physical properties of the surfaces, but also the overall characteristics required for the photothermographic materials.